The alt.usage.english FAQ

"billions and billions"

(Phrase Origins)

Carl Sagan (1934-1996), in his last book _Billions & Billions_
(Random House, 1997, ISBN 0-679-41160-7), admitted that in the
TV series _Cosmos_, first aired in 1980, he "pronounced 'billions'
with a fairly plosive 'b'" to distinguish it from "millions". But
he asserted that he never used the phrase "billions and billions"
in that show, and that the public association of him with that
phrase is due to a parody that Johnny Carson did of Sagan on _The
Tonight Show_.